The present invention relates to an openable roof structure for utilization in such large scale facilities as baseball stadiums, sports arenas, and the like.
In the past, large scale athletic facilities such as baseball stadiums and sports arenas were generally not equipped with a roof. However, in recent years, there has been a demand for a structure which may be utilized regardless of the weather conditions. For example, a film material formed from glass fiber coated with a resin having as its main component tetrafluoroethylene resin (i.e., Teflon resin), has been used as a roof. Facilities utilizing this structure, which expands in response to air pressure, have been utilized. Furthermore, roof structures in which it is possible to achieve all degrees of opening have been proposed in response to the need for a rigid roof.
However, in facilities of the type mentioned above, not only athletic events, but a variety of other types of events, i.e., concerts, etc., as well are held. Therefore, it is desirable to have an ability to adjust the lighting, acoustics, etc., of the internal environment in response to the type of event being held. However, neither the facilities having air film structure roofs, nor the facilities having openable roofs which have been proposed in the prior art up to now, have been able to provide this feature.
For example, the film which is used as the roof material in air film structure roofs, is thin, allowing the transmission of light. As a result, facilities provided with this kind of roof structure have the advantage of making it is possible to utilize natural illumination. However, this structure presents a disadvantage when it becomes necessary to block natural light. It is not possible to darken the interior of the facility during the afternoon hours. Accordingly, functions at which it is necessary to provide a darkened interior (concerts, for example, where lighting effects are considerably important) cannot be held in the afternoon, presenting a considerable inconvenience.
Furthermore, in the openable roof structures which have been proposed in the prior art up to now, in the case where a film material is used as the roof material, disadvantages similar to those of the air film structure roof occur. On the other hand, when opaque metal plating is used as the roof material, while it possible to darken the internal environment even during the afternoon, this type of structure does not respond to the demand for a degree of natural lighting to be present even when the roof is shut, as when a baseball game is held on a rainy afternoon. In such a situation this type of structure presents a disadvantage in that it becomes necessary to rely completely on artificial lighting.
Furthermore, in all of the above cases, the acoustic character, i.e., reverberation time, etc., within the facility is almost entirely determined by the character of the roof and the ceiling. Therefore, the acoustics cannot be appropriately adjusted in response to the type of event being held.
Given the openable roof structures of the prior art, or air film structure roofs, it is not possible to freely adjust the environment within the facility to create appropriate conditions for the type of event being held. As a result, the usage of these facilities is restricted, presenting a serious disadvantage.
Furthermore, in the movable roof structures proposed in the prior art up to now, because extremely large scale roofs are being moved, high cost expenditures are necessary in order to ensure the safety of the roof structure. The operational costs required in order to drive the machinery for moving the roof increase, while at the same time, the opening and closing action of the roof is not carried out in a timely manner. Accordingly, it has previously not been possible to obtain a superior openable roof structure economically.